The object of this invention is a hydrostatic clutch.
It is known how to provide a hydrostatic clutch by means of a hydraulic pump the flow capacity of which is made to vary if, for example, the pump casing is connected to the driven member while the pump shaft is the driving member, and it will be appreciated that when the pump flow is zero, the pump shaft and its casing are hydraulically locked, and they rotate substantially at the same speed; while when the pump flow is maximum, the shaft rotates and the casing is stationary. Many hydrostatic clutches have been realized by application of this general principle, but for so doing, the pump used has to meet the following imperative requirements:
(a) When the driving member and the driven member are connected to each other (clutched condition), the internal leakage of the pump, the pumping elements of which are made stationary or substantially stationary by a hydraulic locking, must not be resucked by the pump, since this would cause a rapid warm-up of the liquid leading to the destruction of the pump.
(b) The pump has to be self-starting and it must remain in operation even at the highest pumping conditions which are considered.
(c) The pump has to be operable in the two rotation directions.
(d) In its unclutched condition, the pump should present a negligible residual torque.
For the reason of these various imperative requirements, it has not been hitherto possible to provide a hydraulic clutch by means of a piston pump, the pistons being either radial or axial, while this type of pump is that allowing the smallest internal leakage.